Image formation as used in camera obscura and photography dates back to the pinhole camera discovery, experiments, descriptions, and developments of Chinese philosopher Mozi (470 BC to 390 BC), Greek philosopher Aristotle (384 to 322 BC), and Iraqi scientist Ibn al-Haitham (965-1039 AD). As depicted in FIG. 1a, reflected or emitted light from objects or light sources in a scene radiate in all directions, but a small pinhole aperture limits the rays of light to those collinear with both the pinhole aperture and the object or source in the scene. Light rays in other directions are blocked and thus prevented from scattering into the aforementioned collinear rays. The collinear rays then project undiffused and without commingling into the region on the other side of the pinhole aperture where at any distance they can be projected onto a surface, albeit with various distortions (due to irregularities in the aperture shape, degree of curvature of the projection surface, etc.) and at low light intensity (since most of the light rays are by necessity prevented from traveling through the aperture. Moving the projection surface closer to the pinhole aperture makes the projected image smaller and brighter, while moving the projection surface farther from pinhole aperture makes the projected image larger and dimmer. The image forms naturally at any distance by virtue of the organization of the light rays passed through the pinhole aperture. In recent years CCD cameras using pinhole apertures rather than lenses have become commercially available.
In more modern mainstream forms of optical systems, a lens or system of lenses is employed for image formation for light passing through an aperture. A simple representative example is depicted in FIG. 1b, wherein objects or light sources in a scene radiate light in all directions and a significant angular sector of this is captured by a lens of material, dimensions, and curvatures to systematically bend the direction of travel of the captured angular sector of radiated light. In particular, the lens material, dimensions, and curvatures are such that all light rays emanating and spreading from a given location on an object or light source within a scene that are captured by the lens are bent so as to converge at a single point on the opposite side of the lens. In particular, the lens material, dimensions, and curvatures are characterized by a constant f (called the focal length), and if the distance between the lens and an object or light source within a scene is of the value A, the image forms in focus at a point at distance B on the opposite side of the lens where 1/A+1/B=1/f (this relation known as the “Lens Law”). At distances on the opposite side of the lens that are shorter than the distance B, the light rays have not yet come close enough to converge, causing an out of focus image. At distances on the opposite side of the lens greater than the distance B, the light rays have crossed each other and are spreading apart, also causing an out of focus image.
Both these approaches require a significant separation distance between the (lens or pinhole) aperture and the image formation surface. Physical limitations of these and other aspects of camera technology thus create a required appreciable depth or thickness of the optical imaging system. They also require all light for the resulting image to pass through an aperture.
The linear image sensors employed in fax machines, PDF™ scanners, and many types of digital photocopiers use direct and localized-transfer “contact” imaging arrangements. A geometrically-linear array of light sensors are positioned effectively directly upon a flat object such as a paper document that illuminated from the sides or other in other ways. Significant angular sectors of light radiating from a given spot on the flat object are captured by an extremely local light sensor element in the linear array of light sensors. An example of this is shown in FIG. 1c. In many embodiments, each light sensor individually captures the light value of a single pixel of the final generated image. In most fax machines, PDF™ scanners, and many types of digital photocopiers, the geometrically-linear image sensor array is either moved over the surface of the flat object (as in a scanner) or the flat object is moved over the geometrically-linear image sensor array (as in a fax machine). These are suggested in the depiction of FIG. 1d. 
This differs from the lens and pinhole imaging systems (which require a central aperture and free propagation space as the image formation mechanism) represented by FIGS. 1a-1b and the contact imaging systems (which require close to direct contact with the object an arrangement coexistent with illumination) represented by FIGS. 1d-1e. In this system a spatial array of light sensors (typically relatively large, for example with height and width dimensions of a few inches) performs measurements on the incoming light field, and imaging is obtained numerically.